High data rate, power efficient, indoor infrared wireless communication links are difficult to reliably economically establish due to multi-path effects. Wireless networks operated in indoor mobile environments can provide much more flexibility in (computer) communication networking, office automation, and integrated service digital networks. Infrared transmission for this application has the advantage of being able to accommodate large information capacity. However, high rate (20-20M bps and up) communication links are difficult to reliably establish for indoor wireless infrared channels due to the following considerations:
Power-limited communication channels. PA1 Requirements for power efficiency for a portable unit/transceiver. PA1 Strong multi-path effects for high rate systems. PA1 Simple, economical and practical receiver structure. Consequently, a bandwidth-limited communication environment. PA1 Modulation PA1 Coding PA1 Equalization PA1 Synchronization
There are four main issues in designing communication systems for the physical layer of this kind of communication network.
There are a number of patents directed to the design of communications systems, each having certain advantages and disadvantages. A number of such patents are set forth below.
U.S. Pat. No. 4,599,723 to Eck discloses a technique for redundantly encoding data for synchronous or asynchronous serial transmission or recording and the correlative technique for decoding the serial bit stream are disclosed. The encoding technique involves making the second data string of a data strong pair the complement of the first data string and formatting to the format H.sub.1 DataH.sub.2 Data where H.sub.1 and H.sub.2 are headers wherein at least one bit is the same in corresponding bit positions of the headers. Decoding involves first detecting the headers and then checking to confirm that the data fields are complements. Also disclosed is a technique for extracting bits from the data stream.
U.S. Pat. No. 4,375,101 to Cerrocchio discloses a system for formatting data on video tape for high accuracy recovery in which binary data is recorded on the video signal track of video tape in a prearranged format of three redundant blocks of data words between successive vertical sync pulses. Each redundant block of data words is preceded by a set of at least three redundant sync words and the last block of data words is followed by a fourth set of redundant sync words. The redundant sync words in each set are separated from each other by a plurality of blank horizontal sync pulses intervals. Circuitry for recovering data in this format is disclosed together with a system for writing data in this format.
U.S. Pat. No. 4,518,947 to Poston et al discloses a method and apparatus for decoding a redundantly coded digital signal wherein each information character is coded with a plurality of signal elements. Each of the signal elements is sampled by an analog to digital converter and the resulting sample value is transmitted to an adder. The sampled value is added to an accumulated sum which is received from a storage circuit. The sum of the sampled value and the accumulated sum is transmitted through a selector switch to both a decision circuit and the storage circuit. After the last of the redundant coded signal elements is sampled and the sampled values included within the accumulation sum, the state of the information character is determined by the decision circuit. The switch then enters a null data set to reset the accumulated sum to zero for processing the next group of redundantly coded signal elements.
U.S. Pat. No. 4,464,714 to Huijses et al discloses a system for transmitting digital information comprising a coding arrangement, a transmitting medium such as a record carrier, and a decoding arrangement. In such a system, the digital information is received in groups of input words which are converted, in the coding arrangements, into code words representing the input words. Each code word corresponds to an input word, and is arranged for application to the transmission medium, the code words being applied to the decoding arrangement via the transmission medium and then converted back into digital information in the decoding arrangement.
According to the present invention, data is encoded per symbol period as code-words comprised of gray-code constrained sequences of pairs of duplication subcodes and complementary check bits in adjacent time slots of the symbol period. A guard slot is added as the last time slot in each symbol period.